1. Field of the Invention
The present invention relates to a P- and Ti-added galvannealed steel sheet which has high strength and good ductility. The present invention relates also to a process for producing said galvannealed steel sheet.
2. Description of the Related Art
Automotive steel sheet often calls for good press workability as well as good corrosion resistance. Steel sheet meeting these requirements is exemplified by galvannealed steel sheet. This steel sheet is formed from a cold-rolled steel sheet (as base material) by hot-dip galvanizing and heat treatment at about 600.degree. C. for improvement in adhesion between the plated layer and the base material. This heat treatment turns the plated layer into alloy.
For improvement of galvannealed steel sheet in press workability, it is necessary to improve adhesion between the plated layer and the steel sheet (as base material) and it is also necessary to improve the press workability of the steel sheet itself. For the steel sheet to have good deep drawability, the base material should be Ti-added killed steel sheet in which carbon in the steel solid solution is fixed by titanium.
Recent automobiles strongly call for weight reduction for improvement in fuel efficiency. The base material for galvannealed steel sheet calls for press workability as well as higher strength. The latter requirement is usually met by adding a solid solution hardening element (such as P, Mn, and Si) as disclosed in Japanese Patent Publication No. 21334/1994.